1. Field of the Invention
The invention relates to a device for sensing an obstacle in the opening range of a powered movable closure element of a motor vehicle, more particularly an electrically powered window pane or sunroof. The device is provided with at least one sensor electrode generating an electrical field in the opening range of the closure element. In addition, the device is provided with a control unit for detecting a change in the capacitance of the sensor electrode caused by a change of the electrical field as a result of the presence of an obstacle in the opening range of the closure element and for providing a control signal for a drive powering the closure element.
2. Background Art
Devices of this kind are guards serving to prevent part of the human body being trapped between a powered window pane and at least some part of the edge surrounding the window pane. For this purpose known devices feature a sensor which senses the presence of an obstacle in the opening range of the window pane representing a closure element and furnishes a signal controlling the drive powering the window pane. As regards the function of the sensor a distinction is made between guards requiring physical contact with the obstacle such as, for example, as described in DE 199 13 105 A1 and guards working by proximity (non-contact) sensing.
Known from EP 1 154 110 A2 is a proximity or non-contact type guard. The way in which this guard works is based on a change in capacitance of an electrical field generated between two electrical conductors prompted by an electrically conducting obstacle. One of the two conductors, the sensor electrode, is integrated in a weatherseal sealing the closure element and receives a predefined electrical charge. In this way a reference capacitance can be determined between the sensor electrode and the other conductor, the basic electrode, which, for example, may be grounded. The change in the reference capacitance due to the obstacle is detected by means of a control unit which furnishes a control signal for a drive powering the closure element.
Furthermore, DE 296 16 654 U1 reveals a device for sensing obstacles that includes a sensor consisting of a piezoelectrical cable connected to a control unit. The piezoelectrical cable produces an electrical tension signal in case of radial as well as axial pressure or strain, the electrical tension signal being proportional to the force produced by the pressure or strain. If such force is produced by an obstacle, for example in the opening range of a gate or window pane, a signal controlling the gate or the window pane can be produced by the control unit.